Presentation on theme: "Potential of Direct Analysis in Real Time Mass Spectrometry for Rapid Characterization of Organic Residues on Ceramics Potential of Direct Analysis in."— Presentation transcript:
Potential of Direct Analysis in Real Time Mass Spectrometry for Rapid Characterization of Organic Residues on Ceramics Potential of Direct Analysis in Real Time Mass Spectrometry for Rapid Characterization of Organic Residues on Ceramics John Hopkins and Ruth Ann Armitage Department of Chemistry, Eastern Michigan University, Ypsilanti, MI, USA 48197 Introduction Methods Future work Acknowledgments References This work was supported by the National Science Foundation under MRI-R 2 award #0959621 Thanks to the following people for support and materials for future studies: Laura Banducci, Anthropology Department, University of Michigan Leah Minc, Oregon State University Radiation Center Silas Hurry and Tim Riordan, Historic St. Mary’s City Landrea Standfield (EMU student) and Chip Cody, JEOL USA Additional support provided by the EMU CAS Dean’s Travel Fund, EMU Chemistry Department, and the EMU Provost’s Undergraduate Research Stimulus Program. b Conclusions Some biomarkers of food residues are readily identifiable on ceramics with this method, regardless of exposure to a burial environment or cleaning. Olive oil was the most easily identifiable residue. Capsaicin seems to be extremely sensitive to soil exposure. Contaminants from handling ceramics without gloves and from storing sherds in plastic bags are readily observable by DART-MS. DART-MS appears to have potential for screening samples to determine those best suited for further study. However, it is not a replacement for other methods for a full, quantitative analysis of residues. Chemical analysis of residues on archaeological ceramics provides significant insights into how humans utilized food resources in the past. The methods most commonly used yield large amounts of diagnostic information, but are both time consuming and expensive. DART-MS, which requires little or no sample preparation and can be carried out in minutes, has the potential for screening large collections of ceramics for further study with other methods. Existing methods of residue analysis are time consuming and expensive, and not all sherds will still have meaningful residue: –Biodegradation –Desorption of residue from sherd –Contamination from handling of artifacts can make accurate characterization impossible –Ceramic may not have a residue from usage A method for rapidly identifying residues on pottery will allow for sample “triage.” –Determine which sherds have identifiable residue. –Select a set of samples known to have usable residue for further analysis. Prepare simulated sherds –Residues were prepared by placing approximately 15 mL of liquid in a shallow terra cotta ceramic dish and allowing the material to soak in. –The ceramic dish was then broken into four or five pieces. Two pieces of the ceramic were buried for up to six months, and two subjected to analysis without burial. One of each subjected to a standard field cleaning treatment for excavated sherds. Sample analysis –Abrade interior surface of sherd near rim. Five mg of resulting powder and 15 microliters of methanol combined to form a paste. –The ceramic/solvent pastes were introduced on the closed end of a melting point capillary tube by placing the tube directly into the gap between the DART source and the mass spectrometer orifice. –Minimal sample preparation needed. –DART-MS is sensitive for small molecules (<1000 Da) –Positive ion mode generally applicable, forms M+H + –Negative ion mode has higher sensitivity for acids, forms M-H - –AccuTOF MS yields high resolution spectra. To evaluate the efficacy of DART-MS for screening of authentic archaeological ceramics, we need to answer three questions about our simulated ceramic residues: 1.Can the biomarker compounds be reliably identified after food has been applied to ceramic surface? 2.Can residue biomarkers be identified after short-term burial (1 week – 6 months)? 3.How do standard cleaning techniques affect the ability to identify biomarkers using DART-MS? Current methods for identification include FTIR and LC-MS/MS. Expected biomarkers: Tartaric Acid Polyphenols, i.e. malvidin and syringic acid. Stable isotope mass spectrometry coupled to GC-MS is the method of choice for identification of the source of adsorbed lipids Expected biomarkers: Fatty acids, oleic and linolenic Di- and triacylglycerols The savory flavor of garum derives primarily from glutamate. LC-MS is the primary identification technique. Thai fish sauce and garum colatura from Italy were used as modern equivalents to the Roman condiment. Expected biomarkers: Amino acids, such as glutamic acid. Olive Oil “Roman” food residues Can common foods from Roman cultures be identified on ceramics with DART-MS? GarumWine “Mesoamerican” food and plant residues Fruits of Capsicum annuum have been an important food in what is now Mexico for approximately 8000 years, as indicated by the presence of chili pepper remains in Oaxacan pottery. Residue: Habañero chili, chopped finely and boiled in water to make residue High capsaicin content Residues of xocolatl beverages have been identified on ancient ceramics using HPLC or HPLC-MS Residue: Cocoa powder boiled in water ~ 10 min. Theobromine and caffeine serve as biomarkers for chocolate in N. Central and S. America. The cleaning procedure removed most or all of the pyroglutamic acid, evidenced by the loss of signal in those samples. The buried ceramics also showed no evidence of the pyroglutamic acid. Other amino acids, including leucine, valine, and proline were observed PGlu is much less, or absent Olive oil does not have a single diagnostic biomarker, so the DART mass spectrum of the neat oil was compared to the residue. Oleic and linoleic acid, were the largest peaks observed in the extra virgin olive oil used in our study. Lipids are easily identifiable after burial and cleaning. Diacylglycerols persist after cleaning and burial, and provide the best diagnostic signal for olive oil. Is there really tartaric acid on the ceramic? Peak at m/z 149.026, 20 mmu difference Expect maximum 10 mmu difference 6 mo buried ceramic showed possible tartaric acid. Unclear if tartaric acid is actually present in all of the wine residues’ spectra with a significant mass difference, or if the signal at 149.026 Da arises from a different component of the wine or soil. Future studies will focus on understanding this problem and developing a method for identifying syringic acid rapidly by DART- MS. Can common foods and plants from the Americas be identified on ceramics with DART-MS? CacaoChili peppers Corn (maize) Tobacco Caffeine Caffeine can come from other sources like coffee or tea – Theobromine is highest in cacao, but present in other plants. Even after 6 months of burial and cleaning, a small, distinct theobromine signal (0.7% abundance) remains. – Cleaning did not seem to affect the total theobromine signal for buried ceramics. Theobromine Sherds are routinely handled (fingerprints) and stored in plastic zip-top bags. – Erucamide is a slip agent in plastic bags. – Squalene is a hydrocarbon; primarily from fingerprints. Cleaning removes capsaicin (unexpected- not very water soluble) Storage and handling of ceramics is critical for DART-MS analysis of residues, as the method is surface specific. Nicotine has been identified using GC and LC-MS on a variety of artifacts. Curently working on nicotine identification at realistic concentrations. We will be evaluating the method on 17 th c. pipes from Historic St. Mary’s City during Summer 2012. Even after cleaning, nicotine remains the base peak of the spectrum. Is there a reliable biomarker compound for fermented corn that could be used to rapidly identify residues of chicha? 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